I have configured a cluster of two VSP-4000 through vIST link, I can see one is Master and the second is slavefrom switch Edges I cannot ping IP mgmt of slave vsp, however I can ping the master, is this normal scenario ?

Also can I force vsp1 to be slave and vsp2 to be master (and vice versa) through CLI ?

first - the vIST design does not have an master/slave design - both members are active.You have to decide which L3 redundancy for your clients you want to deploy.My recommendation would be RSMLT (edge-support).I assume that your VSP cluster is configured correctly and the vIST status is UP.